The deployment of expandable structures into interior body regions is well known. For example, expandable structures, generically called "balloons," are deployed during angioplasty to open occluded blood vessels. As another example, U.S. Pat. Nos. 4,969,888 and 5,108,404 disclose apparatus and methods the use of expandable structures for the fixation of fractures or other osteoporotic and non-osteoporotic conditions of human and animal bones.
Many interior regions of the body, such as the vasculature and interior bone, possess complex, asymmetric geometries. Even if an interior body region is somewhat more symmetric, it may still be difficult to gain access along the natural axis of symmetry.
For example, deployment of an expandable structure in the region of branched arteries or veins can place the axis of an expandable structure off-alignment with the axis of the blood vessel which the structure is intended to occupy. As another example, insertion of an expandable structure into bone can require forming an access portal that is not aligned with the natural symmetry of the bone. In these instances, expansion of the structure is not symmetric with respect to the natural axis of the region targeted for treatment. As a result, expansion of the body is not symmetric with respect to the natural axis of the targeted region.
It can also be important to maximize the size and surface area of an expandable structure when deployed in an interior body region. Current medical balloons manufactured by molding techniques are designed to be guided into a narrow channel, such as a blood vessel or the fallopian tube, where they are then inflated. In this environment, the diameter of the balloon is critical to its success, but the length is less so. Such balloons only need to be long enough to cross the area of intended use, with few constraints past the effective portion of the inflated balloon. This allows conventional balloons to be constructed in three molded pieces, comprising a cylindrical middle section and two conical ends, bonded to a catheter shaft. As a practical matter, neither the length of the conical end, nor the length of the bond of the balloon to the catheter shaft, affect the function of conventional balloons, and these regions on conventional balloons are often 1 cm in length or more. Indeed, the larger the balloon diameter, the longer the end cone, which creates a tradeoff between maximum effective length and maximum effective diameter. This tradeoff makes optimization of conventional structures problematic in interior structures with defined lengths, such as bone.